Neuronal migration plays a key role in the formation of the vertebrate brain. Migrating neurons must respond to both long-range directional signals and local environmental cues. An excellent system for studying this process is the highly stereotyped migration of the facial branchiomotor (ibm) neurons in the zebrafish hindbrain. The vertebrate hindbrain is segmented through the activity of Hox genes along its anterior-posterior axis into seven reiterated domains, the rhombomeres. The Ibm neurons arise in rhombomere 4 (r4) of the hindbrain and migrate posteriorly along the midline to r6 and r7. Upon reaching these posterior rhombomeres, the Ibm neurons undergo a dorsal and radial migration to reach their final positions. I propose to study the migration of Ibm neurons as a model to dissect how migrating cells pass through local environments with different regional identities. I will test whether Ibm neurons alter their segment identity to cross rhombomere boundaries during their migration (Aim 1). I will determine the role of Hox genes in specifying Ibm migratory behavior (Aim 2). I will also conduct a genetic screen to identify genes that are required for proper Ibm neuron migration (Aim 3). Understanding the molecular mechanisms underlying this neuronal migration is of general significance since the interactions between migrating cells and the local environment are fundamental to directed migration [unreadable] [unreadable]